The German Football Federation (DFB) president has sent an open letter to all 25,641 clubs in the country urging respect for referees after a volunteer linesman was beaten to death in the Netherlands.

Dutch police have arrested four players suspected of involvement in the fatal beating after a youth match.

DFB president Wolfgang Niersbach said the news of the beating was received "with horror and disbelief."

Niersbach said what happened in the Netherlands must not repeat itself anywhere in the world. He said the commitment of referees in Germany "deserves the highest recognition and respect" and "our special protection."

Without them, there would be no regulated nationwide football, with its 1.6 million games annually, Niersbach said.